The present invention relates to novel naphthopyran materials. More particularly, this invention relates to indeno-fused photochromic naphthopyran materials and to compositions and articles comprising such naphthopyran materials. This invention also relates to naphthols used in making the novel naphthopyrans. When exposed to light radiation containing ultraviolet rays, such as the ultraviolet radiation in sunlight or the light of a mercury lamp, many photochromic materials exhibit a reversible change in color. When the ultraviolet radiation is discontinued, such a photochromic material will return to its original color or colorless state.
Various classes of photochromic materials have been synthesized and suggested for use in applications in which a sunlight-induced reversible color change is desired. Although indeno-fused photochromic naphthopyrans are known, it has unexpectedly been discovered that materials demonstrating a bathochromic shift in the visible lambda max and/or an increase in sensitivity, which is measured as a change in optical density over time, can be prepared.